Dynamometric measuring device for a drill pipe

ABSTRACT

A dynamometric measuring device for a drill pipe which includes, firmly attached to the rotating pipe, sensors disposed in a groove on the pipe and electronics for conditioning the signals supplied by the sensors. The measurement signals are transmitted by a commutator-fixed brush assembly to a fixed, non-rotating part. By providing follower-amplifiers of very low output impedance on the commutator, rotating, portion of the assembly and follower-amplifiers of very high input impedance on the fixed brush side of the assembly, the transmission of signals is carried out at zero current. To assure high quality signal analysis, a separation circuit on the fixed brush side of the assembly separates the DC and AC components of the signal prior to transmission to the surface.

The present invention concerns a dynamometric measuring device for adrill pipe.

To produce a dynamometric device to measure forces and stresses exertedon the drill pipe, the major problem is not to take the measurement butto transmit it under optimal conditions to the data-acquisition unitresponsible for processing it. Thus, taking into account the length ofthe cables linking the measuring unit to the data-acquisition unit, itis essential to guard against all conceivable causes of deterioration ofthe signals to be transmitted.

Furthermore, it is necessary to transmit the electrical signals from therotating assembly constituted by the drill string to a fixed referencepoint constituted by the mast.

Finally, it is necessary to take steps to prevent the transmittedsignals from being distorted by the passage from the moving parts to thefixed parts.

A first object of the invention is therefore to alleviate at least oneof these disadvantages.

This object is achieved by the fact that the dynamometric measuringdevice for a drill pipe comprises, firmly attached to the rotating pipe,sensors and electronics for conditioning the signals supplied by thesesensors, these electronics being firmly attached to the rotating parts,the sensors being disposed in a groove and the measurement signals beingtransmitted to a fixed part by a rotating commutator-fixed brushassembly, the crossing of the commutator-brush assembly being carriedout at zero current.

According to another feature of the invention, the measurement signalsfrom each sensor are transmitted by a channel constituted by anindependent track and an earth track, each of the two tracks being incontact with a double pair of brushes, each brush having acharacteristic resonant frequency.

According to another feature, the device comprises sensors for measuringthe traction, the torsion, the longitudinal and transverseaccelerations, the temperature and the speed of rotation of the drillpipe.

Another object of the invention is to ensure a compromise between themaneuverability and the location of the electronics.

This object is achieved by the fact that the electronics, firmlyattached to the rotating parts and connected between the sensors and therotating commutator, are constituted by amplifier stages of low outputimpedance for each measurement channel.

According to another feature, the power supply to the rotationallydriven electronics is ensured by two supplementary channels.

Another object of the invention is to improve significantly theinformation, from the sensors, that one can exploit.

This object is achieved by the fact that a second electronic circuit ismounted on the fixed part connected to the brushes, this electroniccircuit comprising, on the output side of each brush, a stage offollower-amplifiers of very high input impedance.

Another object of the invention is to limit to a minimum the number ofcompatible channels while maintaining the highest quality of signalanalysis.

This object is achieved by the fact that the second electronic circuitcomprises, on the output side of each follower-amplifier, a separationcircuit for the DC component and a separation circuit for the ACcomponent of the signal.

According to another feature of the invention, the separation channel ofthe DC component comprises a low-pass filter of cut-off frequency equalto 10 kHz in series with a line amplifier.

According to another feature of the invention, the separation channel ofthe AC component comprises a capacitor for cutting off the DC component,in series with a variable band-pass filter having a lower cut-offfrequency of 0.1 Hertz and an upper cut-off frequency of 1 kHz and inseries with the line amplifier.

Another object of the invention is to constitute a device that isreliable, sealed and flameproof.

This object is achieved by the fact that the assembly is mounted in avolume limited at its ends by upper and lower collars which are mountedso as to rotate with respect to the drill pipe and to form a seal, and acylindrical sheath of length corresponding to the distance separatingthe upper and lower collars so as to form a sealed annular space betweenthe drill pipe and the interior of the sheath.

Other features and advantages of the present invention will appear moreclearly on reading the description below given with reference to theattached drawings in which:

FIG. 1 represents an overall view of the dynamometric measuring device;

FIG. 2 represents the block diagram of the electrical and electroniccomponents of the assembly;

FIG. 3A represents the diagram of the rotating electronic circuitsituated on the input side of the brush-commutator;

FIG. 3B represents the diagram of the fixed electronic circuit situatedon the output side of the brush-commutator;

FIG. 4 represents the diagram of the power supply part of the electroniccircuit.

The dynamometric measuring device is placed on a drill pipe (1) in aspace delimited by an upper collar (110) mounted so as to rotate and toform a seal with respect to the pipe by means of a bearing (11).Likewise, a lower collar (120) is mounted so as to rotate, by means of abearing (12), on the pipe (1). A sheath (100) is then put into place toform a sealed volume delimited by the upper collar (110), the lowercollar (120) and the internal diameter of the sheath (100).

On the inside of the annular volume included between the sheath (100)and the pipe (1) are disposed, in a groove (10) of the pipe (1),traction gauges (60,61), a pair (70,71) of gauges forming a torsiongauge, a temperature gauge (50), a pair of longitudinal accelerometers(20,21) and three transverse accelerometers (40,41,42). Each of thesegauges constitutes a measurement channel. An electronic circuit (3) forprocessing the signals supplied by these various sensors is mounted,firmly attached to the drill pipe (1), on the inside of the volumedelimited by the collars. Above the groove (10) and firmly attached tothe pipe (1) is mounted a set of tracks forming a rotating commutator(80). A pair of tracks is associated with each measurement channel. Thesignals delivered by each pair of tracks are taken by two pairs ofbrushes associated with each channel and represented by the reference(81). The brush support assembly (81) is firmly attached to the uppercollar (110) which is itself firmly attached, by means of a rotatingstop-arm, to the fixed part constituted by the drilling mast. Thebrushes are connected to a second electronic circuit for processing thesignals from each measurement channel of which the outputs are fed via aconnector (90) to a power cable of N pairs individually screened by anouter screen for N/2 measurement channels. The signals delivered by thesensors (20,40,70,60) are fed to a first electronic circuit (3) situatedon the input side of the rotating commutator (80) and of the fixed brushassembly (81). The signals recovered by the fixed brush assembly (81)are fed to an electronic circuit (9) situated on the output side ofthese signals, and the outputs of this electronic circuit are fed to anADF connector (90) for transmission to the screened cable. In additionto each measurement channel constituted by a pair of tracks of therotating commutator, the commutator-brush assembly comprises two otherpairs of tracks for the purpose of transmitting the supply from thefixed electronic circuit to power the sensors and the rotatingelectronic circuit (3).

A first pair of tracks of the commutator (80) is connected by acapacitor (395), as shown in FIG. 4. This pair of tracks supplies on oneside a voltage of +12 volts and on the other side the earth to therotating electronic circuit. The pair of tracks is connected to a doublepair of brushes (81) connected to the terminals of a capacitor (955),which is itself connected in parallel to the terminals of a capacitor(954). This capacitor (954) is connected on one side to the output of aregulating circuit (953) and on the other side to one of the terminalsof a capacitor (952) of which the other terminal is connected to theinput of this regulating circuit (953). Another capacitor (951) is alsoconnected in parallel between the terminals of the capacitor (952).Finally a self-protecting device (950) is connected in parallel to theterminals of the capacitor (951) and receives, by the connector (90), onone side the supply of +18 volts and, on the other side, the earth.

A circuit identical to the one shown in FIG. 4 and bearing the reference(96) will be used to constitute the negative-supply of -12 voltsnecessary for the functioning of the sensors and of the rotatingelectronics (3).

A measurement channel of the device constituting the electronic circuit(3) situated on the input side is shown in FIG. 3A. This measurementchannel comprises a gauge (20) constituted, for example, by a Wheatstonebridge constituted by a combination of four resistances (20,31,32,33).The diagonal of this bridge is connected, on one side to the positiveterminal, and on the other side to the negative terminal of adifferential amplifier (34), while the other diagonal of this Wheatstonebridge is connected, on one side to the +12 volt supply, and on theother side to the -12 volt supply. The output of the differentialamplifier (34) is connected to the positive input of a seconddifferential amplifier (35) of which the output is looped back to itsnegative input. This second amplifier (35) constitutes a follower stageof very low output impedance. The output of this amplifier (35) is fedonto one ring of the commutator assembly (80), the other ring of thecommutator constituting the measurement channel is formed by the earth.

The signal fed by the pair of rings is taken by a double pair of brushes(81, FIG. 3B) and fed to the positive input of a differential amplifier(91) of which the output is looped back to its negative input. Theoutput of this amplifier (91) is fed, on one side to a circuit (92) forextracting the DC component, and on the other side to a circuit (94) forextracting the AC component of the measurement signal. These stages arefollowed by a line amplifier and protection stage. The amplifier (91)constitutes a follower stage of very high input impedance. Thecombination of follower stage of low output impedance with the followerstage of very high input impedance situated respectively on the inputand output sides of the commutator-brush assembly, ensures that themeasurement signals are transmitted at zero current. This allows arelatively wide pass-band to be used and the precision of themeasurement to be retained, although the state of cleanliness or of wearof the discs and brushes of the commutator constitutes the principalsource of noise within the dynamometric measuring device. Moreover, theseparation of the DC components and the AC components, and the finalamplification of the latter before transmitting, allows a significantimprovement to be made to the information which is going to besubsequently exploited. The separation stage of the DC components of themeasurement signals is an integrating circuit that performs twofunctions. First, it acts as a low-pass filter passing only that portionof the input measurement signal having a frequencies below 10 kHz.Second, the integrating circuit integrates, or averages, the filteredsignal to derive the DC component. The integrating circuit is formed bya resistance (920), a capacitor (921), and a line amplifier (930). Asdepicted in FIG. 3A, resistance (920) is mounted in parallel withcapacitor (921) between the output of the amplifier (91) and earth. Thecommon point of resistance (920) and capacitor (921) is connected to thepositive input of the line amplifier (930). The output of the lineamplifier is looped back to its negative input. The output of lineamplifier (930) is fed to resistance (931) of which the output isconnected on one side to the connector (90) and on the other side toearth via a protection element (932), such as, for example, a Zenerdiode. The circuit (94) for extracting the AC component is constitutedby a capacitor (940) connected to the output of the amplifier (91). Thiscapacitor (940) is connected at its other side to earth by a circuitconstituted by a resistance (941) in series with a capacitor (943). Thecommon point of the resistance (941) and the capacitor (943) isconnected on one side, by a resistance (942), to the negative input of adifferential amplifier (945) and on the other side, by a resistance(947), to the output of this amplifier (945). The output of theamplifier (945) is also connected by a capacitor (946) to the negativeinput of the latter. The positive input of the amplifier (945) isconnected by a resistance (944) to earth. The output of this amplifier(945) is fed to a low-pass filter constituted by a resistance (922)connected by a capacitor (923) to earth. The common point of theresistance (922) and the capacitor (923) is connected to the positiveinput of a line amplifier (930) of which the output is looped back tothe negative input. The output of this amplifier is fed to a resistance(931) connected, on one side, to the connector (90), and on the otherside by a fuse (932) to earth. The capacitor (940) makes it possible toeliminate the DC component of the signals and the circuit constituted bythe amplifier (945), the resistances (941,942,944,947), the capacitors(943, 946) constitute a band-pass filter having a lower cut-offfrequency of 0.1 Hz. and an upper cut-off frequency of 1 kHz.

The separation of the DC and AC components, and the final amplificationof the latter before transmission allows the information that one canexpect to exploit after measurement to be significantly improved. Forexample, the separate transport of the DC component and of the ACcomponent amplified 300 times allows one to expect a signal-to-noiseratio 300 times greater after transmission.

Assuming that this AC component is subsequently processed by a digitalunit, this is a non-negligible increase in resolution which is madepossible by the technique of separating the DC and AC components of thesignal.

The separation of the DC and AC components is carried out on the outputside of the commutator to reduce the number of commutator rings and thusthe volume and the cost of the device.

The device so constructed results in less space being required, aminimum number of parts, and optimum reliability and quality ofmeasurement.

Finally, the presence of as many line amplifiers as channels to transmiton the input side of the connector device (90) makes it possible toimprove the characteristics of the transmitted signals and in particularto reduce the level of noise from the transmission, especially theequipment ages. Moreover, the protection stages provided either at theoutput stages, that is to say after the line amplifiers, or at the powerinput stages, protect the equipment against hazards in the field or moresimply against interference arising from lightning or from switching inlarge electric machines located in the vicinity.

Other modifications of the invention, available to a person skilled inthe art, also come within the spirit of the invention.

We claim:
 1. Dynamometric measuring device for a rotating drill pipecomprising:a plurality of sensors disposed in a groove in the rotationdrill pipe, each of said sensors providing means for outputting ameasurement signal over a respective measurement channel; a firstelectronic circuit attached to the rotating drill pipe for conditioningthe signals supplied by these sensors and including a stage offollower-amplifiers of very low output impedance; a commutator-brushassembly for transmitting the signals from the first electronic circuitattached to the rotating drill pipe to a fixed part, saidcommutator-brush assembly including a commutator mounted on the rotatingdrill pipe and a fixed-brush assembly mounted on the fixed part; and asecond electronic circuit mounted on the fixed part, wherein saidcircuit comprises on an output side of the fixed-brush assembly, meansincluding a stage follower-amplifiers of very high input impedance forreceiving said signals transmitted to the fixed part and for therebycausing transmission of the signals from the first electronic circuitattached to the rotating drill pipe to be carried out at zero current,and, on an output side of each follower-amplifier, a separation circuitfor a DC component and a separation circuit for an AC component of eachof said signals.
 2. Device according to claim 1, wherein the signal fromat least one measurement channel supplied by each sensor is transmittedby an independent track of the commutator and an earth track.
 3. Deviceaccording to claim 1, wherein a power supply to the first electroniccircuit is ensured by two supplementary channels.
 4. Device according toclaim 1, wherein the electronics, attached to the rotating parts andconnected between the sensors and the rotating commutator, areconstituted for each channel by an amplifier stage of low outputimpedance.
 5. Device according to claim 4, wherein said plurality ofsensors measure the traction, the torsion, the longitudinalaccelerations, the transverse accelerations, the temperature and thespeed of rotation of the drill pipe.
 6. Device according to claim 1,wherein the separation circuit for the DC component comprises a low-passfilter of cut-off frequency equal to 10 kHz in series with a lineamplifier and a protection element.
 7. Device according to claim 1,wherein the separation circuit for the AC component of the signalcomprises a capacitor for cutting off the DC component in series with avariable band-pass filter having a lower cut-off frequency of 0.1 Hertzand an upper cut-off frequency of 1 kHz, a line amplifier and aprotection circuit.
 8. Device according to claim 1, wherein the assemblyis mounted in a volume limited at its ends by upper and lower collars,which are mounted so as to form a seal and to rotate with respect to thedrill pipe, and a cylindrical sheath of length corresponding to thedistance separating the upper and lower collars so as to form a sealedannular space between the drill pipe and the interior of the sheath.